西双版纳热带季节雨林凋落叶分解与土壤动物群落：两种网孔分解袋的分解实验比较

 以西双版纳热带湿性季节沟谷雨林混合凋落叶作为分解基质，在不同位置季节雨林样地，采用不同网孔（ 2和0.15 mm）分解袋，开展大中型土壤动物对雨林凋落叶分解影响的实验，测定了不同网孔分解袋土壤动 物多样性、凋落叶分解速率和主要养分元素释放状况。结果显示：2 mm网孔分解袋土壤动物类群相对密度 年均值为2.67～2.83目?g－1凋落物干重，个体相对密度年均值为22.3～21.77个?g－1凋落物干重，显著 高于0.15 mm网孔分解袋的类群相对密度0.27～0.28目?g－1凋落物干重和个体相对密度2.88～2.77个?g－ 1凋落物干重（p<0.01），并且0.15 mm网孔分解袋中极少量的动物个体主要为小型类群弹尾目和蜱螨目（ 原生动物、湿生土壤动物线虫不计），由此我们视2 mm网孔分解袋凋落叶分解由绝大多数土壤动物和其它 土壤生物共同作用，而0.15 mm网孔分解袋基本排除了大中型土壤动物对袋内凋落叶分解的影响。2 mm网 孔分解袋凋落叶物质失重率（71%左右）、分解率指数（1.88～2.44）和主要养分元素释放率明显高于 0.15 mm分解袋（34%～35%，0.48～0.58）。通过比较两种不同网孔分解袋凋落叶失重率和元素释放率的 差异，显示出季节雨林大中型土壤动物群落对凋落叶物质损失的贡献率为年均值46%左右，并使凋落叶C/N 和C/P明显降低，而对不同元素释放率的影响不同，其中对N、S和Ca元素释放率的影响较大，而对K素释放 的影响作用最小。相关分析显示，2 mm网孔分解袋内土壤动物群落类群和个体的相对密度与凋落叶物质残 留率有较好的负相关关系，而群落香农多样性指数与凋落叶分解率指数表现出一定的正相关关系。

SOIL FAUNA AND LEAF LITTER DECOMPOSITION IN TROPICAL RAIN FOREST IN XISHUANGBANNA, SW CHINA: EFFECTS OF MESH SIZE OF LITTERBAGS

Background and Aims The influence of soil fauna on litter decomposition is rarely exploredin tropical rain forest. This study examined the effect of soil fauna on the decomposition of mixed substrate by litter bag technical at two tropical seasonal rain forest plots in Xishuangbanna, SW China in year of 2000. The following questions were considered in the present study: 1) What roles do soil fauna play in regulating litter mass loss and decomposition rate? 2) How do soil fauna influence litter nutrient release? Methods In order to examine the role of soil macro_mesofauna in mass loss and nutrient release of litter, litter bags with both fine mesh size (0.15 mm) that excludes the soil macro_mesofauna population from litter and coarse mesh size (2 mm) that allows soil fauna access to litter were used in this experiment. Mass loss and C, N, P, S, K, Ca, and Mg concentrations of leaf litter were determined from the litter in two different mesh size litterbags at monthly intervals. The soil fauna were extracted by hand and by heating the samples.  Key Results Higher relative density and taxonomic diversity of total soil fauna were found in the bags with 2 mm mesh size (22.3-21.77 individuals and 2.67- 2.83 orders per g of dry litter) compared to the bags with 0.15 mm mesh size ( 2.88-2.77 individuals and 0.27-0.28 orders per g of dry litter). Collembola and Acari were the most abundant group, and Hymenoptera(ant), Coleoptera, Hemiptera, Diptera, Diplopoda, Isopoda, Araneae, Pseudoscorpiones were common groups of soil fauna in litter bags with 2 mm mesh size. There were very few individuals of Collembola and Acari in the 0.15 mm litter bags. Our results suggested that soil macro_mesofauna contributed more to the decomposition of leaf litter in 2 mm litter bags than that in 0.15 mm litter bags. The higher mass loss rate (aroun d 71%), decomposition rate (k=1.88-2.44), and nutrient release in litter ba gs with 2 mm mesh size than in litter bags with 0.15 mm mesh size (34%-35%, k=0.48-0.58) indicated a significant influence of soil macro_mesofauna on mass loss and nutrient release in tropical seasonal rain forest. The release rates of N, S and Ca that could be attributable to the soil macro_mesofauna were higher than other elements whereas K release rate that could be attributable to the soil macro_mesofauna was the lowest. Soil macro_mesofauna caused greater decreases in C/N and C/P ratios in litter bags with 2 mm mesh size than litter bags with 0.1 5 mm mesh size. There were negative relationships of the percentage of litter mass remaining with order richness and individuals abundance of soil fauna. However, a positive relationship between Shannon_Wiener index of soil fauna and the decomposition rate was found.  Conclusions This study suggests that the presence of soil fauna accelerated plant litter decomposition in the tropical seasonal rain forest. The litter mass loss attributable to the soil macro_mesofauna was about 46%. The effects of soil macro_mesofauna on the nutrient release rates were different among elements. The diversity of soil fauna may have important ecosystem consequences, particularly in tropical rain forest.